The ability of the auditory system to analyze a sound into its component frequencies, frequency analysis or resolution, underlies many types of complex auditory perception. The purpose of this project will be to examine the development of this ability in the first year of infancy. Although some earlier work has addressed the issue, it is not clear how sensory and nonsensory factors contribute to the performance of infants in the tasks used to measure frequency resolution. In the proposed work, three psychoacoustic measures of frequency resolution, varying in susceptibility to nonsensory performance factors, will be obtained from three groups of infants, tested longitudinally at 3, 6, and 12 months of age. In the first experiment, the effects of increasing signal level on the infant's ability to discriminate frequencies will be tested in order to determine how age-related changes in absolute sensitivity might influence discrimination. In the second experiment, psychophysical tuning curves, a measure of frequency resolution requiring detection rather than discrimination, will be generated. This measure will allow for assessment of task effects on measures of frequency analysis and will also provide additional information about frequency selective response when the masker frequency is at some distance from that of the signal. However, since psychophysical tuning curve widths may be affected by response bias effects, a third experiment is proposed, in which detection thresholds for a tone masked by comb-filterd noise will be obtained. This measure, although not as informative as the psychophysical tuning curve, will provide a check against possible response bias effects.